1. Field of the Invention
The present invention relates generally to nuclear, biological or chemical (NBC) warfare. The invention relates more particularly to a system for purifying air contaminated by NBC agents for supply to persons inside a shelter, vehicle, or aircraft. More specifically, the invention relates to the further concentration of the purified air into oxygen suitable for use in high-altitude aircraft or for medical purposes.
2. Description of the Related Art
Sorption systems are a well established means of providing effective protection against chemical warfare agents. The sorbent bed through which contaminated air is passed contains highly porous particles which adsorb and retain toxic chemical vapors. First used in World War I, sorbent beds of activated carbon have become the primary defense against the threat of a chemical warfare attack. Impregnants have been added to the activated carbon to increase its sorption capacity for chemical warfare vapors.
Low pressure impregnated carbon bed filters are most suitable for individual protection due to their simplicity. For collective protection, however, they present serious limitations. As they are not regenerable, the impregnated sorbent beds must be replaced at regular intervals which represents a significant logistics support problem. Low pressure filters must be constructed with large cross sectional flow areas in order to limit the particle attrition and sorbent dusting resulting from excessive flow velocities. This results in a poor configuration for installation purposes.
The presently used ASC "Whetlerized" carbon has a limited life in the field. The impregnated carbon beds are easily contaminated and can be rendered non-effective even under non-combat conditions. Moisture and heat can adversely affect the carbon impregnants, and normal atmospheric contaminants such as hydrocarbon vapors and exhaust fumes can poison the sorbent beds prior to a chemical warfare attack.
The major operating advantages of activated carbon, as compared to many proposed alternative means of controlling toxic vapors, is the universality of the present ASC activated carbon (at least when fresh) in handling the present range of acknowledged NBC agents. To provide more complete protection, the activated carbon beds are used in conjunction with a high efficiency particulate air (HEPA) filter or aerosol barrier to remove liquid aerosols, dust particles, biological agents and sorbent fines that may be contaminated with toxic chemicals.
For use in high-altitude aircraft and for medical purposes, the oxygen content of air must be concentrated. A molecular sieve pressure-swing adsorber has been developed for oxygen concentration. See U.S. Navy Molecular Sieve On-Board Oxygen Generation System--An Update, NACD-8021-60, Oct. 1978.
Historically, the provision of large quantities of medical grade oxygen has been a critical component in the successful treatment of combat medical casualties. In modern warfare as defined by the Air Land 2000 Doctrine, an increased volume of oxygen will be needed to treat nerve agent casualties via inhalation and respirator therapy. For use in such a highly mobile tactical environment, preferably the oxygen would be concentrated on site, but the ambient air would most likely be contaminated by NBC agents.